Five Things Homeowners Should Know About Roof Sheathing Before Getting Their Roofs Replaced

Kenneth Wilson

Replacing or installing a new roof is a big undertaking, and there’s a lot to think about. For instance, you might be in two minds about whether or not it’s necessary to install roof sheathing underneath your chosen material.

To help you decide whether roof sheathing will be a good addition to your home, we introduce you to five important considerations and provide you with an overview of the price you can expect to pay for its installation.

But let’s begin by looking at what roof sheathing actually is and why it might be an important addition to your property.

What Is Roof Sheathing?

Roof sheathing is the robust layer of wooden boards that are fixed underneath your roof. Roofers attach shingles or other materials, such as lead or tile, to the sheathing when fixing a roof, so it’s a crucial part of the roofing process.

Sheathing can be comprised of various types of wood, but it’s important you use the correct material, or it may rot and be less durable. Ultimately, getting your roof sheathing right is so important, or you could risk the entire structural integrity of your roof.

Five Things You Need to Know About Roof Sheathing

1. The Material You Choose is Important

In most instances, roofers opt for oriented strand board or plywood for roof sheathing. Oriented strand board is the cheaper option and is more lightweight, but it’s more than adequate for various shingles and composite roof options.

However, if you’re opting for a heavier material for your roof, you will need to go for plywood, as it’s much more durable. Although it will cost you more, plywood is the better option for sheathing when you opt for the likes of slate or tile on the roof of your home.

2. Roof Sheathing Improves the Strength and Structure of Your Roof

The primary purpose of roof sheathing is to strengthen your roof and ensure it doesn’t fall in on itself. The sheathing is typically attached to the joints and trusses within your roof and helps to ensure your roof doesn’t sag or bow because of the elements (like snow).

Properly installed sheathing also makes sure that weight is evenly distributed across the roof. Although shingles are lighter than other roofing materials, they’re heavier than you might expect. Roof sheathing provides an additional layer of support for the even distribution of weight across the entire roof.

3. Sheathing Also Prevents Leaks & Improves Fire Retardancy of Your Home

In the early days of asphalt shingles, sheathing wasn’t typically included in the roofing project. Roofers (and homeowners!) quickly learned that roofs without sheathing were much more prone to leaking, as the additional layer of wood acts as a barrier against rainwater seeping through.

Equally, roof sheathing offers additional protection against fire, as it makes it more difficult for fire to spread to the roof. While not entirely flame resistant, including roof sheathing can make your property more fire retardant.

4. Make Sure You Seal Your Roof Sheathing

One mistake that homeowners occasionally make is that they forget to seal the individual boards of plywood or oriented strand board before proceeding with the next stage of the roofing project. This enables water to permeate through the boards and means your sheathing is less sound from a structural perspective.

But the good news is that sealing your sheathing is a relatively simple process. While there are several ways to do it, simply affixing roofing tape across the joints of your sheathing should do the trick. Most roofers complete this as standard, but it’s worth remembering if you’re undertaking roof sheathing as a DIY project.

5. Understand When Roof Sheathing Needs to Be Replaced

Although roof sheathing is built to last, it isn’t bulletproof. At some stage, you will need to replace your roof sheathing, so it’s important that you don’t neglect this responsibility to try and save a few bucks. You will need to replace your roof sheathing in the following instances:

  • If it is notably cracked or damaged
  • If your roof is visibly bowing or sagging under weight
  • If you identify a leak that is coming from your roof
  • If the wood has started to rot
  • If you’re installing a new roof

While roof sheathing that has been correctly installed should stand the test of time, it won’t last a lifetime. The above tell-tale signs indicate that you should replace your sheathing, and it’s best to do it sooner rather than later.

How Much Does Roof Sheathing Cost?

When it comes to budgeting for roof sheathing, you need to consider it from a couple of perspectives. The first is whether you’re installing sheathing afresh or whether you’re installing it as part of a roof repair.

For instance, Home Advisor informs us that it costs between $3.50 and $7.20 per square ft to install plywood or OSB siding. When you consider the size of a standard roof, you can expect to pay anywhere between $1,500 and $3,700 to install roof sheathing that is made of plywood or OSB.

As mentioned, OSB is typically cheaper than plywood, so if you’re looking for a more affordable roof sheathing option, then OSB is your best bet. While the above prices consider the cost of installation, they don’t take into account the cost of repairing your roof.

If you’re replacing (or installing) roof sheathing because of a fault in your roof, you will have to pay somewhere in the region of $376 - $11,648 to repair your roof first, according to Home Advisor. Your roof repair costs are determined by the scale of the damage, the size of the area that needs to be replaced, as well as the material that you’re replacing.

You will need to factor in your repair costs alongside your budget for installing roof sheathing, as there’s no point in installing wooden sheathing under a roof that is damaged.

Final Thoughts

Whether you’re looking to install sheathing in a new roofing project or are aiming to replace the sheathing within a damaged roof, doing so is important and will improve the structural integrity of your home. Hopefully, the five tips and the price guide above will help you as you prepare to install roof sheathing and will help you understand what to expect.

Kenneth Wilson
November 22, 2021
Contractor Tips, Roofing

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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